High Power Very Small Tri(s)-10'-14'-why not?

Discussion in 'Multihulls' started by Doug Lord, Jun 27, 2010.

  1. Doug Lord
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    Doug Lord Flight Ready

    The daggerboard and rudder resist leeway as they do on most other trimarans. Sailing angle is adjustable(see previous post-the one with all the numbers). Probably about 6-13 degrees will be optimum.
     
  2. Munter
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    Munter Amateur

    On a regular tri the task of minimizing leeway is shared between the lee float and the centerboard. Presumably a short planing float will not contribute much to this task. Further, when heeling to leeward, the lifting foils will not be opposing leeway as they would with windward heel. I suspect that the little tri will heel significantly more than the figures you propose and that the loading up of the vertical foils will exceed the point where they ventilate.
     
  3. Doug Lord
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    Doug Lord Flight Ready

    -------------------------------------
    Thats where DESIGN comes into it. The altitude control system would be designed to maintain a set angle pretty closely. You may not understand this concept too well-it is sometimes similar to the "multihull with veal heel"(see sketch below and note the windward foil) concept in that there will be times when the foils are pulling down to make up for lighter than maximum crew weight. In that case there is a component of the down lift that is to weather. In the case where the foil is operating only as pitch control, with little force applied either up or down by the wand/flap, it may pay to use a rotating daggerboard-as does the Capricorn F18.
    At any rate if the boat is designed properly the system should work. If there is a screw up then it would be fixed during testing. Thats what prototype development is-no need to accept a mistake-just fix it.

    1) Note: as it was on the F18 killer 18' tri the use of lifting foils on the daggerboard and rudder with a wand based altitude control system is the key to allowing this boat to function. It would not work without this system as an integral part of the design-same on the 18' tri.
    http://www.boatdesign.net/forums/multihulls/18-trimaran-vs-f18-catamaran-33201-5.html see page 5

    2) Note: Orma tris use curved foils in the ama and those foils are designed to support 60-70% of the boats weight. The ama and the curved foil develop very little lateral resistance-thats why those boats use long daggerboards in the main hull.

    click on image: (note there is a force vector arrow from the intersection of the weather power foil vertical fin and the lifting foil pointing to weather-its hard to see but it is there....this illustrates how the main foil on the little tri would work when sailed with less than maximum crew weight.)
     

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  4. Munter
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    Munter Amateur

    I find little in your responses to address my previous concerns though I acknowledge that you are trying.

    Sin(6) = 0.1 so an inclined foil at that angle will have 10% of it's area stopping side slip. 90% of the force generated will be downforce. At 13 degrees heel this improves to 20%. However, this dynamic downforce now needs to be supported by the leeward planing float. We now have (100kg boat, 80kg skipper + say 40kg downforce) all being supported on a the planing float. I thought the original idea of the foils was to reduce the need to support the full boat's mass on the float? Now we seem to be requiring the float to support more than the boat's mass.

    In eany event, 10% of the foil area doesn't sound like an effective way to resist leeway. Further, this solution only applies when the main hull requires down force. What happens when that isn't the case? Only a fraction of the vertical area remains in the water and to make things more difficult, they are operating with high pressure differences between the sides at the air/water interface making ventilation more likely.

    With reference to your continued assertion that the boat's target weight is realistic (and even conservative at 55 kg!) and noting that you've made no attempt to reject my suggestion that mass is related to volume, why not try scaling the boat's mass by the cube of beam instead of length. After all, what makes length more important than beam when you're dealing with a squarish platform? If we take this approach the cubic rule of thumb tells us that the mini tri will be 180 kg based on a 100kg Weta. Why is this any less valid?

    Your first (and repeated with minor edits) post says "its remarkable what is possible". I don't think you've really shown anything other than it is possible to dream up a set of numbers that ignore the physical contraints using arm waving and simple rejection of critical input to arrive at fairy tale make-believe solution. How about real solutions to the problems of mass, leeway and bouyancy?

    I don't want to kill your joy here but I think your excitement over the concept is premature and that there are significant issues that need to be addressed before you could reasonably consider this any kind of a step forward. How about demonstrated achievement first, then hype and celebration instead of the other way around?
     
  5. Doug Lord
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    Doug Lord Flight Ready

    ===================
    I don't think you are reading what I've written.

    1) I showed that there is plenty of latitude in terms of weight by adjusting max crew weight down and/or SA up.

    2) lateral resistance by daggerboard and rudder with a contribution from the main foil when pulling down. You speak of a "fraction" of the fin in the water and you imply that it is too low a fraction to develop the needed lateral resistance-on what basis? I haven't said what the area of the vertical fin is or what "fraction" is in the water at between 6 and 13 degrees angle of heel for the boat. The fact that the hydrofoil will contribute to windward ability along with the possible use of a gybing board are both pluses. Note that the Moth unloads the daggerboard almost 100% at 15 degrees angle of heel.
    You should rest assured that when(if) the boat is designed and built there will be plenty of lateral resistance though it will be tweaked to be the minimum required for excellent upwind work.

    3) I think this is a simply obnoxious comment that ignores my detailed answers and the facts as I have presented them. It is just plain BS and very disappointing.

    4) I used the accepted method to scale the WETA's weight down. From a direct comparison standpoint the WETA is designed for almost twice the load and two third's more SA.(see Weta specs below) It's main hull is gigantic compared to the main hull of this boat. I think my weight target is realistic .The Weta is designed for much higher loads than the MXP-11-the WETA RM is TWICE that of the little boat and must be built to heavier scantlings to be strong enough.
    WETA RM=5100ft.b at max load.
    MXP-11 RM = 2550ft.lb. at max load


    5) As I have said numerous times these are preliminary TARGET numbers with wide latitude to be changed and still have the ratios shown. For instance, hull weight could be increased by 70lb and still leave enough capacity for a 174lb person at the ratios shown with no adjustment in SA. You either don't understand "target numbers" or choose to ignore their meaning. Based on #3 above the latter is likely the case.
    ----------------------
    =================
    Weta specs:
    Sail area – main 8.3 m2 ~ 89.4 ft2
    Sail area – jib 3.2 m2 ~ 34.5 ft2
    Sail area – gennaker 8.0 m2 ~ 86.1 ft2
    Total SA= upwind 123.9
    upwind + downwind=210sqft =1.61 X MPX-11 (161.5% more)
    PERFORMANCE

    Crew capacity 200 kg ~ 440 lbs =1.83 X MPX-11( 183.3% more)
    ================





    Pix-daggerboards on tri's: ( note than on the MPX-11 sailing angle is not determined just by the wind-it is preset and controlled automatically.)
     

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  6. Paul B

    Paul B Previous Member

    Well Munter, did you expect anything less?


     
  7. Munter
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    Munter Amateur

    Still more hand waving and dismissal (combined with a few unnecessary personal insults to capture the outrage) rather than consideration of the critique. It does seem to be par for the course for Doug's concept threads Paul. Though the tone of my last email was indeed condescending, I had hoped for something better.

    I also think there are a few issues with the figures quoted in Doug's vitriolic response.

    Sail area figures for the Weta are quoted and compared to the mini-tri, presumably in an attempt to indicate how this design is moderate compared with an existing design. It seems to me though that the comparison is being done between the Weta downwind sail (220) and the mini tri upwind sail (130 - though it isn't specifically nominated as upwind or down). If you compare the Weta upwind with what appears to be the mini-tri upwind the mini-tri has more sail despite being shorter. You seem to be using the 130 figure to determine ratios on sail carrying power and the ability to plane upwind so i assume this is the upwind sail area. It wouldn't make much sense to use the downwind sail area to work out if the boat would plane upwind.

    The concept target figures show a boat that is wider and has more sail, includes bench seats (comfortable), lifting (and occasionally providing downforce) hydrofoils and a folding mechanism over and above the weta spec but somehow comes in at half the weight despite the use of carbon in the Weta to keep the weight down. Continued reference to the boat's target mass at 55 kg in the face of multiple reasonable arguments to the contrary seems unjustified to me. If these are target numbers why not develop them with critical input?

    With reference to resisting leeway - I specifically used the term fraction because I don't know the proportion of the foils area that will be lifted from the water. The term fraction implies less than the whole. If some foil is lifted then less than the whole is in the water - I think it difficult to argue against this though it seems to have raised your ire as an unreasonable assertion. The pictures of tris you have provided all show them in situations where a large proportion of the foils is out of the water and indeed the boats appear to be sailing well but have you noticed that the floats are contributing to resisting leeway? The flat planing floats in the mini-tri concept don't appear to contribute in the same way so the load would remain on the vertical foils. When flying the main hull, a fraction of the original vertical foil area is now taking the full leeway load which I predict will result in ventilation. I see no acknowledgement of this concern regarding the contribution from the floats in your responses.

    Your reference to moth foils "unloading" at 15 degrees appears to be a snippet you have copied from somebody else's experience on the web as I understand you have never sailed a moth. I'm not sure how it is relevant given that a moth tilts to windward and, as best I can tell, your tri tilts to leeward. Are you suggesting that at 15 degrees of leeward tilt, the formerly horizontal foil will now provide the full quotient of leeway resistance? Isn't this effect contingent on the foil pulling downwards? As previously asked, what happens when the foil isn't pulling downwards? The load returns to the verticals I presume (and this is ok because of the photos attached to your previous post?)

    Doug - surely you posted this concept because you sought feedback from others interested in the same topic. Unfortunately is appears that giving feedback is futile and merely results in assertions of ignorance of your self anointed design supremacy. If you won't take feedback from other group members then the only point at which you will discover the hard realities of physics that I think will cause your concepts to under perform to expectations is when you build and actually sail something. Physics appears to have undermined the performance of the a-skiff and resulted in it's quick and apparently permanent disassembly. Comfortingly for you, now that the a-skiff has been honourably retired the next reality check appears a long way off.
     
  8. Doug Lord
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    Doug Lord Flight Ready

    When you make comments like this and this in the face of detailed responses -you effectively end any discussion at all:


    I have made every attempt to answer your questions in detail. It has been a waste of time. In this post and the last post you repeat a question that has been answered and that proves conclusively to me that whatever answer I give is unacceptable to you. So be it....

    ===================================
     
  9. Munter
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    Munter Amateur

    Doug,
    Your purported "detailed responses" are nothing of the sort. Lets take boat mass for example. I believe this is one of the issues you believe has been resolved. As I see it the sequence of events went like this:

    You put forward a 55kg target mass.
    I responded by saying that seems too light
    You said, "I used the cubic rule"
    I explained the basis for the cubic rule (volumetric) and explained why it wasn't appropriate (your boat's volume is unlikely to be one half that of a Weta)
    You said "I used the cubic rule - this is the accepted method"
    I said " If we're going to blindly follow a rule of thumb why don't we cube the beam - its just as valid and the boat comes out at over three times your target weight"
    You said "I told you - I used the cubic rule"
    I said "Your boat isn't comparable with the data point you are using for the cubic rule as it has many more components and is larger in beam, has hydrofoils, comfy lounges and more sail area therefore the cubic rule is not appropriate"
    You said "Your comments are obnoxious and that's BS"
    I said "I don't think your boat will work and that is consistent with your other projects"
    You said "It is impossible to satisfy your demands"

    Enough you said, I said. Do you get the point? I am reading what you write but on the whole there aren't any answers there. That is what I refer to as hand waving.
     
  10. Gary Baigent
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    Gary Baigent Senior Member

    By St. George and the Messiah Doug, you've painted yourself into a broken glass corner surrounded by frothed up asbestos. Your only hope now is to actually build, then weigh ... doesn't matter if the hi powered Flying 11 is an overweight dog - there will actually be a piece of three dimensional sculpture there ... and congratulations, we'll all line up to .... actually touch it.
     
  11. Doug Lord
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    Doug Lord Flight Ready

    =============================
    You're funny.......

     
  12. Doug Lord
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    Doug Lord Flight Ready

    =================
    Gary, do you read?

    --
    PS-Hows the Roto-Tri coming?
     
  13. science abuse
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    science abuse Junior Member

    Here's a company that's currently producing foiled and unfoiled small tris:
    http://www.windrider.com/rave.shtml

    I love the idea... to an extent. To me, the whole point of having a small tri is the tramp surfaces. The ability to have some extra space and stability on a boat that fits next to your car in the garage.
    The 12 and 10 footers look just as cramped as a mono would be, moreso really, because the main hull is so narrow. The short ones look more like beginners boats with training wheels.
    I'd rather like to try a 15-17 foot beachable "weekender", ketch rigged with storage space (food, water, sleeping bag etc). Something you can spend all day sailing and not get cramps, the ketch rig allowing you to balance the boat out for minimal inputs. Drag it ashore and camp for the night, or sleep aboard if weather permits.
    Then again, I'm weird.
     
  14. Doug Lord
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    Doug Lord Flight Ready

    =========================
    SA, there are a lot of boats out there that would fit the bill or could be easily modified to do so. I'm interested in seeing what is possible if a trimaran is designed to use a lot of power-between 60 and 100% of the power possible with a square tri with two people on trapezes. It hasn't been done in small tri's under 18' and I'm convinced it can be and lead to new and exciting ways to sail. A tri just using 60% of the available power in the above configuration could be designed to sail faster than an equivalent length beach cat with MUCH more comfort. It is an area of trimaran design largely unexplored and that fascinates me. Thanks for your post!
     

  15. science abuse
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    science abuse Junior Member

    If I may, once the crew is up on their trapezes, the two windward hulls flying.... wouldn't the center hull basically be dead weight?
     
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